While the billionaire businessman continues to dominate the polls, he took serious heat from all sides during the second Republican presidential debate here, with Trump's rivals managing to get in their punches—and airtime—during the second showdown.

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Only Scott Walker, desperate to reverse his free-fall in the polls after a programmed, uninspired performance in last month’s debate in which he gave back time to the moderator, seemed to fully disappear on the stage, getting less camera time than everyone but Mike Huckabee. Walker finished with just 7:10 speaking time.

Trump, amazingly, went quiet for a 37-minute stretch after sparring with Jeb Bush over foreign policy.

The CNN-hosted showdown was seen as a high-stakes endurance test, with the primetime debate at the Reagan Presidential Library stretching three hours, with only one bathroom break for the candidates. It was also a more grand test of staying power—those with subpar performances may see their hopes permanently fade in a sprawling primary fight where fundraising dollars and media coverage are at such a premium.

Bush, who loosened up as the debate progressed, had spent weeks preparing for a showdown with Trump, who has portrayed the establishment favorite as a “low energy” candidate and forced his campaign to completely recalibrate.

After Bush was asked why most of his foreign policy advisers came from his father’s and brother’s administrations, Trump saw an opening: “Your brother’s administration gave us Barack Obama,” he said, prompting Bush to prove that he, too, can counter-punch.

“As it relates to my brother,” he said, pausing for a moment. “There’s one thing I know for sure: he kept us safe.”

Interestingly, mentioning his biggest political liability brought Bush’s loudest applause of the night.

But Carly Fiorina, who was given a spot in the primetime debate after her improved standing in the polls following her standout performance last month in the undercard debate, landed the strongest punches against Trump of anyone.

Fiorina got the first question of the night and opted not to take the bait and slam Donald Trump. But when Fiorina was asked to respond to Trump’s “Look at that face” remark disparaging her appearance, she was devastatingly succinct.

“Trump says he heard Mr. Bush very clearly,” Fiorina said, playing off Trump’s critique of Bush’s statement earlier this summer that “women’s health issues” are overfunded. “I think women all over this country heard very clearly what Mr. Trump said,” Fiorina said.

“I think she’s got a beautiful face, and I think she’s a beautiful woman,” Trump countered, drawing a pained grimace from Fiorina as the telecast went to a commercial break.

Fiorina overshadowed several of the other candidates on the stage—including Walker, Marco Rubio, who again showed his aptitude on foreign policy issues but failed to hit the same rhetorical home runs he did in the first debate, John Kasich, who is looking to replicate his early success in New Hampshire on a national stage, and Rand Paul, who stuck with his libertarian brand of foreign policy that has so far failed to attract much voter interest.

Ben Carson, who was careful not to pick a fight with Trump or any of the other rivals, maintained the calm, steady demeanor that has proved soothing to Republican voters looking for an outsider who's not Trump.

Bush was ready to duke it out with Trump; and he defended himself from one of the billionaire’s most pointed attacks—that he’s a puppet controlled by the donors who’ve helped him build a $120 million war chest—by asserting that Trump tried to buy him when he was governor of Florida.

“He wanted casino gambling in Florida,” Bush said, gesturing to Trump at the lecturn to his right.

“Yes, you did,” he continued as Trump sought to cut him off. “I’m not going to be bought by anybody.”

“If I wanted it, I would have gotten it,” Trump shot back cooly, noting “the donors, the lobbyists have very strong power over these people.”

As the back-and-forth intensified and Bush looked to speak over Trump, the businessman stopped him in his tracks, reprising his most withering critique. “More energy tonight, I like that,” he said, as Bush smiled to mask his irritation.

When the conversation shifted to immigration reform, the signature issue of Trump’s populist campaign, Bush asked Trump to apologize for drawing his wife into the campaign by alleging that Bush has a soft spot for undocumented immigrants because he’s married to a Mexican-American.

“I won’t do that because I said nothing wrong, but I hear she’s a lovely woman,” Trump responded.

But perhaps the most memorable exchange between Bush and Trump was one full of wry humor. When CNN's Jake Tapper asked everyone for their Secret Service code name, Bush had a quick response—"Eveready."

"It's very high energy, Donald," Bush said of the battery-inspired name, in reference to Trump's constant criticism of the former Florida governor as being low on energy. In a moment of levity, Trump then extended his hand for a low-five, which Bush enthusiastically—or aggressively—slapped.

For long stretches, when the debate focused on substantive policy questions, other candidates tried to break through. Mike Huckabee spoke passionately about religious liberty. Kasich, persistent in his unwillingness to go on the attack, conveyed passion about taking on ISIL and keeping the country safe. Ted Cruz, who disappeared at times, articulated the disgust that many conservatives feel toward the GOP establishment.

“We’re frustrated as conservatives. We keep winning elections and not getting the results we want,” Cruz said.